The present invention relates generally to computer systems and, more particularly, to a method and apparatus for operating a computer system to configure the system via a serial test bus included within the system. The present invention not only permits system configuration via a serial test bus but also permits status monitoring, error logging and comparable operations to be performed via a serial test bus during system operation. The present invention is generally applicable to computer systems and components and, in its broadest aspects, can be utilized within a single integrated circuit.
Historically, initial system configuration has been implemented by physical devices on circuit boards making up the system. For example, switches, plugs, jumpers, connectors and the like were used for configuration. Accordingly, configuration or reconfiguration of a computer system required significant time and the resulting configuration often included errors which required still more time to correct. In addition, the reliability of the computer system was reduced due to the possible failures of the physical configuration devices.
An improved computer system configuration arrangement is provided by using integrated circuit (IC) devices to store system configuration data. The IC devices are initialized by entering configuration data into the devices from an interactive controller which usually retains the configuration data between periods of time when the system is active or until system reinitialization is requested.
In systems with high levels of integration, IC system configuration devices are implemented as application specific integrated circuits or ASICs. The ASICs often do not interface with a system or processor bus and therefore cannot be accessed directly under program control. Therefore, a separate configuration port or bus is needed to interface with the ASICs for configuration purposes. Unfortunately, the provision of a separate configuration bus adds to the cost and complexity of a computer system and also tends to increase the connection points or pin counts required for the ICs or ASICs used to construct a computer system.
Accordingly, there is a need for simple and effective way of accessing the ICs or ASICs of a computer system for system configuration without the requirement of a separate configuration bus. Preferably, the system configuration access arrangement would also provide for other system operations such as status monitoring, error logging and comparable operations within the computer system.